Switching DC-to-DC converters having a multiphase coupled inductor topology are described in U.S. Pat. No. 6,362,986 to Schultz et al. (“Shultz '986”), the disclosure of which is incorporated herein by reference. These converters have advantages, including reduced ripple current in the inductors and the switches, which enables reduced per-phase inductance or reduced switching frequency over converters having conventional multi-phase DC-to-DC converter topologies. As a result, DC-to-DC converters with magnetically coupled output inductors achieve a superior transient response without an efficiency penalty compared with conventional multiphase topologies. This allows a significant reduction in output capacitance resulting in smaller, lower cost solutions.
As discussed in Schultz '986, performance of a DC-to-DC converter utilizing a coupled inductor is affected by the coupled inductor's leakage inductance. Accordingly, it may desirable to customize or adjust a coupled inductor's leakage inductance for the inductor's application.
Some coupled inductors have been proposed. For example, FIGS. 1-3 show one coupled inductor 100 developed by Volterra Semiconductor Corporation. In particular, FIG. 1 shows a side plan view, FIG. 2 shows a cross sectional view, and FIG. 3 shows an end plan view of coupled inductor 100. Coupled inductor 100, which has a height 106, includes a magnetic core 102 and two or more windings 104. FIG. 4 shows a side perspective view of one winding 104.
As another example, Dong et al. propose a two phase “twisted core” coupled inductor in a paper entitled “Twisted Core Coupled Inductors for Microprocessor Voltage Regulators.” However, this coupled inductor has a complex core with poor volume utilization. Additionally, leakage inductance is defined by the distance between vertical core structures and the height of these structures—accordingly, leakage inductance is difficult to control. Furthermore, the twisted core coupled inductor's leakage path makes the inductor's design complex.
Additionally, Dong et al. propose coupled inductors in a paper entitled “The Short Winding Path Coupled Inductor Voltage Regulators.” FIG. 5 shows a top plan view of one coupled inductor 500, which represents the multiphase coupled inductors of this Dong paper. Windings are not shown in FIG. 5 to more clearly show core 502. However, FIG. 6 shows inductor 500 including its windings 602.
Core 502 includes a respective leg 504 for each phase. Each leg 504 has a width 508, and adjacent legs 504 are separated by a window 506 having a width 510. Accordingly, windings 602 have a pitch 604, as shown in FIGS. 6 and 7. Window widths 510 are relatively large and are on the order of leg widths 508. Large window widths 510 are required to provide magnetic flux leakage paths such that leakage inductance is sufficiently large. Leakage inductance is changed by varying the geometry of core 502 and/or by changing window widths 510. Windows 506 also accommodate a respective winding tab, as shown in FIG. 6.
FIG. 7 shows a cross sectional view of inductor 500 along line A-A of FIG. 5. Each area 702 corresponds to the area of a respective leg 504, and each area 704 corresponds to the area of a respective window 506. As seen from FIG. 7, a large portion of coupled inductor 500's volume is not occupied by magnetic material.